python · Python
The message
TypeError: greet() takes 1 positional argument but 2 were given
What it means
You passed one more argument than the function accepts, and when the numbers differ by exactly one it is almost always self. Define a method inside a class as def greet(name): and calling obj.greet("x") sends obj as the first argument, which makes two. If it is a method, change it to def greet(self, name): so it accepts self; if it does not need the instance at all, mark it @staticmethod.
The fix
There is no one-line command for this. The explanation says what to look at instead.
- Printed by
- python
- Python
- 18
A Python traceback splits the answer in two — the last line says what went wrong, the frames above it say where — so reading only the last line gives you the name and loses the place, and for the value-is-missing errors such as NoneType and KeyError the cause almost always sits in a frame above the one that crashed.
Reading an error message
- Read from the first line down. The lower you go the more it is about the tool’s internals; the cause is usually at the top.
- If there is a file and a line number, start there — not the top stack frame, but the topmost line that names a file you wrote.
- Search the message verbatim, but strip your own paths and variable names first; those are what stop the search from matching.
- The same condition is worded differently across tool versions. If results look wrong, add the version number to the query.
- Before pasting a fix, check what it throws away. Some of these cannot be undone.
Common questions
Q. What does “TypeError: greet() takes 1 positional argument but 2 were given” mean?
You passed one more argument than the function accepts, and when the numbers differ by exactly one it is almost always self. Define a method inside a class as def greet(name): and calling obj.greet("x") sends obj as the first argument, which makes two. If it is a method, change it to def greet(self, name): so it accepts self; if it does not need the instance at all, mark it @staticmethod.
Q. How do I fix it?
There is no one-line command. The explanation above says what to look at instead.
Q. Which tool prints this?
python. It sits under Python, and the message runs to 10 words.